Texture and yield strength anisotropy of microalloyed thermomechanically treated high-strength steels

Abstract

The anisotropy of mechanical properties of HSLA steels is due not only to second phases but also to texture in the ferrite. Texture and yield strength anisotropy in the rolling plane were investigated on 2.5-12.5 mm thick thermomechanically treated strip or plate of Nb-, Nb +V-, or Ti-alloyed, pearlite-reduced steels. Relatively strong textures of a predominant {112} <110> type were observed almost independent of alloy type and plate thickness. Yield strength increase from longitudinal to transverse direction showed differences of up to about 50 N/mm2 A qualitative deduction of one part of the yield strength anisotropy from the main texture components can be made using Taylor's theory. The discussion on ferrite, texture-development mechanisms in thermomechanically treated microalloyed steels is based on the γ-a transformation of non-recrystallized textured austenite due to recrystallization hindrance by Nb or Ti. A second source of yield strength directionality, the elongated shape of ferrite grains transformed from non-recrystallized austenite, is discussed, taking into account that the texture did not disappear during normalizing. Second phases such as pearlite bands or sulphide stringers are shown to have no influence on the yield point anisotropy.